Parallax is the apparent displacement of an observed object due to the point of view of the observer. This is an important measurement parameter for various sighting devices especially those incorporating a sighting reticle. For such optical devices, parallax error occurs when the focal plane of the target (or object) image does not coincide with that of the reticle. When parallax error is present, a change in the observer's viewing position will cause the observed target image to appear to move with respect to the reticle cross hairs, thereby inducing an error in sighting registration.
The usual method of measuring parallax error is to translate a telescope across the viewing optics and measure the apparent displacement. Disadvantages of this technique are:
a. A high precision telescope is required that, in itself, must be relatively free of parallax.
b. The technique is generally labor intensive in that a human observer is required or a video imaging system must be adapted requiring constant attention by an operator. Such systems are not suitable for measurement in temperature extremes such as that produced by an environmental test chamber. Care must be taken to insure that the parallax error measured is exclusively that of the system being measured and is not biased by the instrumentation used to conduct the measurement.
c. The degree of resolution in the order of microradians is difficult and expensive to achieve.
Parallax error in certain optical sighting devices such as night sights, varies according to the ambient and operating temperatures of the optical elements and mounting fixtures. A need exists to measure parallax at various temperatures inside of environmental test chambers. The parallax measurement device has been developed to meet this need.
The purpose of this invention is to provide a high precision automated instrument to measure parallax error at various temperatures.